Warm white light emitting diodes (LEDs) with high-color-rendering index (CRI, Ra>80) and low correlated color temperature (CCT<4500K) need a suitable red phosphor. Successful phosphor materials include materials such as Eu2+ or Ce3+ doped (oxy)nitride compounds, for example (Ba,Sr)2Si5N8:Eu2+ and (Ca,Sr)AlSiN3:Eu2+. However, these phosphors have drawbacks when used in certain applications since their emission spectra are broad (full-width at half maximum is approximately 75-85 nm) and a large part of the spectrum is beyond 650 nm in wavelength—a part of the spectrum to which human eyes are insensitive—which significantly reduces the lumen efficacy of LED lighting. MSe1-xSx:Eu materials show red color emission from 600 to 650 nm, and provide high lumen efficacy of LED lighting after combining with yellow or green phosphors. However, the narrow band red phosphors with general composition MSe1-xSx:Eu are hygroscopic, and exhibit rapid deterioration of photoluminescence due to exposure to moisture (water vapor), oxygen and/or heat. Clearly there is a need for narrow band red phosphors with general composition MSe1-xSx:Eu, with coatings which are effective at protecting the phosphor particles from moisture and oxygen and enable a commercially useful phosphor.